Composition of matter and process useful for conversion of hydrocarbons

ABSTRACT

An improved process for converting hydrocarbons using a catalyst which is periodically regenerated to remove carbonaceous deposits, the catalyst being comprised of a mixture containing, as a major component, solid particles capable of promoting hydrocarbon conversion at hydrocarbon conversion conditions, and, as a minor component, discrete entities comprising at least one spinel, preferably alkaline earth metal-containing spinel, and a minor amount of at least one added component selected from the group consisting of alkali metal components, calcium components, barium components, strontium components, beryllium components and mixtures thereof.

This application is a continuation of prior U.S. application Ser. No.615,184, filed May 30, 1984, now abandoned.

BACKGROUND OF THE INVENTION

The present invention is related to the combusting of solid,sulfur-containing material in a manner to effect a reduction in theemission of sulfur oxides to the atmosphere. In one specific embodiment,the invention involves the catalytic cracking of sulfur-containinghydrocarbon feedstocks in a manner to effect a reduction in the amountof sulfur oxides emitted from the regeneration zone of a hydrocarboncatalytic cracking unit.

Typically, catalytic cracking of hydrocarbons takes place in a reactionzone at hydrocarbon cracking conditions to produce at least onehydrocarbon product and to cause carbonaceous material (coke) to bedeposited on the catalyst. Additionally, some sulfur, originally presentin the feed hydrocarbons, may also be deposited, e.g., as a component ofthe coke, on the catalyst. It has been reported that approximately 50%of the feed sulfur is converted to H₂ S in the fluid bed catalyticcracking (FCC) reactor, 40% remains in the liquid products and about 4to 10% is deposited on the catalyst. These amounts vary with the type offeed, rate of hydrocarbon recycle, steam stripping rate, the type ofcatalyst, reactor temperature, etc.

Sulfur-containing coke deposits tend to deactivate cracking catalyst.Cracking catalyst is advantageously continuously regenerated, bycombustion with oxygen-containing gas in a regeneration zone, to lowcoke levels, typically below about 0.4% by weight, to performsatisfactorily when it is recycled to the reactor. In the regenerationzone, at least a portion of sulfur, along with carbon and hydrogen,which is deposited on the catalyst is oxidized and leaves in the form ofsulfur oxides (SO₂ and SO₃, hereinafter referred to as "SOx") along withsubstantial amounts of CO, CO₂ and H₂ O.

Considerable amount of study and research effort has been directed toreducing oxide of sulfur emissions from various gaseous streams,including those from the stacks of the regenerators of FCC units.However, in many instances, the results of this work have left much tobe desired. Many metallic compounds have been proposed as materials topick up oxides of sulfur in FCC units (and other desulfurizationapplications) and a variety of supports, including particles of crackingcatalysts and "inerts", have been suggested as carriers for activemetallic reactants. Many of the proposed metallic reactants loseeffectiveness when subjected to repeated cycling. Thus when Group IImetal oxides are impregnated on FCC catalysts or various supports, theactivity of the Group II metals is rapidly reduced under the influenceof the cyclic conditions. Discrete alumina particles, when combined withsilica-containing catalyst particles and subjected to steam at elevatedtemperatures, e.g., those present in FCC unit regenerators, are oflimited effectiveness in reducing SOx emissions. Incorporation ofsufficient chromium on an alumina support to improve SOx sorptionresults in undesirably increased coke and gas production. EuropeanPatent Publication No. 0045170 discloses the use of discrete entitiescomprising magnesium-aluminum-containing spinels to reduce SOxemissions, e.g., from catalytic cracking units.

Accordingly, an object of the present invention is the provision of animproved composition and process for reducing emissions of sulfur oxide.

An additional object of the present invention is to provide an improvedcomposition and process for reducing the emissions of sulfur oxide fromthe regeneration zones of hydrocarbon catalytic cracking units.

Another object of the invention is to provide an improved hydrocarbonconversion catalyst. These and other objects of the invention willbecome apparent from the following description and examples.

In one general aspect, the present invention involves a process forcombusting solid, sulfur-containing material by contacting the materialwith gaseous oxygen in a combustion zone at combustion conditions toproduce combustion products including sulfur oxide at least a portion ofwhich is sulfur trioxide. The present improvement comprises carrying outthis contacting in the presence of discrete entities containing aneffective amount, preferably a major amount by weight, of at least onemagnesium-aluminum-containing spinel, and a minor, effective amount ofat least one added component selected from the group consisting ofalkali metal components, calcium components, barium components,strontium components, beryllium components and mixtures thereof, saiddiscrete entities being present in an amount sufficient to reduce theamount of sulfur oxide (relative to combustion in the essential absenceof the discrete entities) leaving the combustion zone, e.g, the flue gasemitted from the combustion zone. In a preferred embodiment, the presentdiscrete entities further contain a minor amount of at least one rareearth metal component associated with the spinel to thereby reduce theamount of sulfur oxide (relative to combustion in the essential absenceof the discrete entities) emitted from the combustion zone.

In accordance with another aspect, the present invention involves aconversion process which is carried out, preferably in the substantialabsence of added free hydrogen, in at least one chemical reaction zonein which sulfur-containing hydrocarbon feedstock is contacted withparticulate material to form at least one product, preferably ahydrocarbon product, and sulfur-containing carbonaceous materialdeposited on the particulate material and at least one regeneration zonein which at least a portion of the sulfur-containing carbonaceousmaterial deposited on the particulate material is contacted with gaseousoxygen to combust at least a portion of the sulfur-containingcarbonaceous material and to produce combustion products includingsulfur oxide at least a portion of which is sulfur trioxide. The presentimprovement comprises using a particulate material comprising (A) amajor amount of solid particles capable of promoting the desiredhydrocarbon chemical conversion at hydrocarbon conversion conditions and(B) a minor amount of discrete entities comprising an effective amount,preferably a major amount of weight, i.e., at least about 50% by weight,of at least one magnesium-aluminum-containing spinel, and a minor amountof at least one added component selected from the group consisting ofalkali metal components, calcium components, barium components,strontium components, beryllium components and mixtures thereof, thediscrete entities being present in an amount sufficient to reduce theamount of sulfur oxide in the flue gas from the regeneration zone. It ismore preferred that such discrete entities further comprise a minoramount of at least one rare earth metal, preferably, cerium, componentassociated with the spinel.

In one preferred embodiment, the discrete entities also include a minor,catalytically effective amount of at least one crystallinealuminosilicate effective to promote hydrocarbon conversion, e.g.,cracking, at hydrocarbon conversion conditions. The discrete entitiesare present in an amount sufficient to reduce the amount of sulfuroxides in the regeneration zone effluent when used in a reactionzone-regeneration zone system as described herein.

In one preferred embodiment, the particulate material, more preferablythe discrete entities, further comprise a minor amount of at least oneadditional metal, e.g., a Group VIII platinum group metal, componentcapable of promoting the oxidation of sulfur dioxide to sulfur trioxideat the conditions in the regeneration zone.

The preferred platinum group metals are palladium and platinum, morepreferably platinum.

The preferred relative amounts of the solid particles and discreteentities are about 80 to about 99 parts and 1 to about 20 parts byweight, respectively. This catalyst system is especially effective forthe catalytic cracking of a hydrocarbon feedstock to lighter, lowerboiling products. The present catalyst system preferably also hasimproved carbon monoxide oxidation catalytic activity stability.

The improvement of this invention can be used to advantage with thecatalyst being disposed in any conventional reactor-regenerator system,e.g., in ebullating catalyst bed systems, in systems which involvecontinuously conveying or circulating catalyst between reaction zone andregeneration zone and the like. Circulating catalyst systems arepreferred. Typical of the circulating catalyst bed systems are theconventional moving bed and fluidized bed reactor-regenerator systems.Both of these circulating bed systems are conventionally used inhydrocarbon conversion, e.g., hydrocarbon cracking, operations with thefluidized catalyst bed reactor-regenerator systems being preferred.

The catalyst system used in accordance with certain embodiments of theinvention is preferably comprised of a mixture of two types ofparticles.

Although the presently useful solid particles and discrete entities maybe used as a physical admixture of separate particles, in one embodimentthe discrete entities are combined as part of the solid particles. Thatis, the discrete entities, e.g., comprising calcined microspherescontaining magnesium-aluminum-containing spinel and at least one addedcomponent as described herein, are combined with the solid particles,e.g., during the manufacture of the solid particles, to form combinedparticles which function as both the presently useful solid particlesand discrete entities. The discrete entities in such combined particlespreferably exist as a separate and distinct phase. One preferred methodfor providing the combined particles is to calcine the discrete entitiesprior to incorporating the discrete entities into the combinedparticles.

The form, i.e., particle size, of the present catalyst particles, e.g.,both solid particles and discrete entities as well as the combinedparticles, is not critical to the present invention and may varydepending, for example, on the type of reaction-regeneration systememployed. Such catalyst particles may be formed into any desired shapesuch as pills, cakes, extrudates, powders, granules, spheres and thelike, using conventional methods. With regard to fluidized catalyst bedsystems, it is preferred that the major amount by weight of the presentcatalyst particles have a diameter in the range of about 10 microns toabout 250 microns, more preferably about 20 microns to about 150microns.

The solid particles are capable of promoting the desired hydrocarbonconversion. The solid particles are further characterized as having acomposition (i.e., chemical make-up) which is different from thediscrete entities. In one preferred embodiment, the solid particles (orthe solid particles portion of the combined particles described above)are substantially free of magnesium-aluminum-containing spinel.

In another aspect of the present invention, the discrete entities,whether present as a separate and distinct particle and/or combined withthe solid particles in a single, preferably substantially uniform, massof combined particles further comprise a minor amount of at least oneadditional metal, e.g., platinum group metal, component capable ofpromoting the oxidation of sulfur dioxide to sulfur trioxide at theconditions in the combustion, e.g., catalyst regeneration, zone. Forexample, an effective amount of at least one sulfur oxide oxidationcatalytic component, e.g., metal or compounds of metals selected fromGroup IB, IIB, IVB, VIA, VIB, VIIA and VIII of the Periodic Table, therare earth metals, vanadium, tin, antimony and mixtures thereof,disposed on a support, e.g., one or more inorganic oxides, may beincluded with the present solid particles and discrete entities and/ormay be included on the solid particles and/or discrete entities. Asnoted previously, the sulfur oxide oxidation component may be associatedwith, e.g., deposited on, the spinel component of the present discreteentities.

The composition of the solid particles useful in the present inventionis not critical, provided that such particles are capable of promotingthe desired hydrocarbon conversion. Particles having widely varyingcompositions are conventionally used as catalyst in such hydrocarbonconversion processes, the particular composition chosen being dependent,for example, on the type of hydrocarbon chemical conversion desired.Thus, the solid particles suitable for use in the present inventioninclude at least one of the natural or synthetic materials which arecapable of promoting the desired hydrocarbon chemical conversion. Forexample, when the desired hydrocarbon conversion involves one or more ofhydrocarbon cracking, disproportionation, isomerization, polymerization,alkylation and dealkylation, such suitable materials includeacid-treated natural clays such as montmorillonite, kaolin and bentoniteclays; natural or synthetic amorphous materials, such as amorphoussilica-alumina, silica-magnesia and silica-zirconia composites;crystalline aluminosilicate often referred to as zeolites or molecularsieves and the like. In certain instances, e.g., hydrocarbon crackingand disproportionation, the solid particles preferably include suchcrystalline aluminosilicate to increase catalytic activity. Methods forpreparing such solid particles and the combined solid particles-discreteentities particles are conventional and well known in the art. Certainof these procedures are thoroughly described in U.S. Pat. Nos. 3,140,253and RE. 27,639.

Compositions of the solid particles which are particularly useful in thepresent invention are those in which the crystalline aluminosilicate isincorporated in an amount effective to promote the desired hydrocarbonconversion, e.g., a catalytically effective amount, into a porous matrixwhich comprises, for example, amorphous material which may or may not beitself capable of promoting such hydrocarbon conversion. Included amongsuch matrix materials are clays and amorphous compositions ofsilica-alumina, magnesia, zirconia, mixtures of these and the like. Thecrystalline aluminosilicate is preferably incorporated into the matrixmaterial in amounts within the range of about 1% to about 75%, morepreferably about 2% to about 50%, by weight of the total solidparticles. The preparation of crystalline aluminosilicate-amorphousmatrix catalytic materials is described in the above-mentioned patents.Catalytically active crystalline aluminosilicates which are formedduring and/or as part of the methods of manufacturing the solidparticles, discrete entities and/or combined particles are within thescope of the present invention. The solid particles are preferablysubstantially free of added rare earth metal, e.g., cerium, componentdispersed on the amorphous matrix material of the catalyst, althoughsuch rare earth metal components may be associated with the crystallinealuminosilicate components of the solid particles.

As indicated above, the discrete entities utilized in the presentinvention comprise an effective amount, preferably a major amount, of atleast one magnesium-aluminum-containing spinel.

The spinel structure is based on a cubic close-packed array of oxideions. Typically, the crystallo-graphic unit cell of the spinel structurecontains 32 oxygen atoms. With regard to magnesium aluminate spinel,these often are eight Mg atoms and sixteen Al atoms to place in a unitcell (8MgAl₂ O₄). Other alkaline earth metal ions, such as calcium,stronium, barium and mixtures thereof, may replace all of a part of themagnesium ions. Similarly, other trivalent metal ions, such as iron,chromium, gallium, boron, cobalt and mixtures thereof, may replace allof a part of the aluminum ions.

The presently useful magnesium-aluminum-containing spinels may have amagnesium to aluminum atomic ratio which is not consistent with theclassical stoichiometric formula for such spinel. In one embodiment, theatomic ratio of the magnesium to aluminum in the spinels useful in thepresent invention is at least about 0.17 and preferably at least about0.25. It is preferred that the atomic ratio of magnesium to aluminum inthe spinel be in the range of about 0.17 to about 2.5, more preferablyabout 0.25 to about 2.0.

Further, details on the spinel structure are described in the followingreferences, which are hereby incorporated herein by reference: "ModernAspects of Inorganic Chemistry" by H. I. Emaleus and A. G. Sharpe(1973), pp. 57-58 and 512-513; "Structural Inorganic Chemistry", 3rdedition, (1962) by A. F. Wells, pp. 130, 487-490, 503 and 526; and"Advanced Inorganic Chemistry", 3rd edition, by F. A. Cotton and G.Wilkinson (1972), pp. 54-55.

The magnesium-aluminum-containing spinels useful in the presentinvention may be derived from conventional and well known sources. Forexample, these spinels may be naturally occurring or may be synthesizedusing techniques well known in the art. Thus, a detailed description ofsuch techniques is not included herein. However, a brief description ofthe preparation of the most preferred spinel, i.e., magnesium aluminatespinel, is set forth below.

The magnesium aluminate spinel suitable for use in the present inventioncan be prepared, for example, according to the method disclosed in U.S.Pat. No. 2,992,191. The spinel can be formed by reacting, in an aqueousmedium, a water-soluble magnesium inorganic salt and a water-solublealuminum salt in which the aluminum is present in the anion. Suitablesalts are exemplified by the strongly acidic magnesium salts such as thechloride, nitrate or sulfate and the water soluble alkali metalaluminates. The magnesium and aluminate salts are dissolved in anaqueous medium and a spinel precursor is precipitated throughneutralization of the aluminate by the acidic magnesium salt. Excessesof acid salt or aluminate are preferably not employed, thus avoiding theprecipitation of excess magnesia or alumina. Preferably, the precipitateis washed free of extraneous ions before being further processed.

The precipitate can be dried and calcined to yield the magnesiumaluminate spinel. Drying and calcination may take place simultaneously.However, it is preferred that the drying takes place at a temperaturebelow which water of hydration is removed from the spinel precursor.Thus, this drying may occur at temperatures below about 500° F.,preferably from about 200° F. to about 450° F. Suitable calcinationtemperatures are exemplified by temperatures ranging from about 800° F.to about 2000° F. or more Calcination of the spinel precursor may takeplace in a period of time of at least about one half hour and preferablyin a period of time ranging from about 1 hour to about 10 hours.

Another process for producing the presently useful magnesium aluminatespinel is set forth in U.S. Pat. No. 3,791,992. This process includesmixing a solution of a soluble acid salt of divalent magnesium with asolution of an alkali metal aluminate; separating and washing theresulting precipitate; exchanging the washed precipitate with a solutionof an ammonium compound to decrease the alkali metal content; followedby washing, drying, forming and calcination steps. The disclosure ofU.S. Pat. No. 3,791,992 is hereby incorporated herein by reference.

Other methods of preparing the presently usefulmagnesium-aluminum-containing spinel compositions are disclosed in U.S.Patent applications Ser. Nos. 445,304, 445,305, 445,306 and 445,130which are commonly assigned with this application.

In general, as indicated previously, the magnesium-aluminum-containingspinels useful in the present invention may be prepared by methods whichare conventional and well known in the art.

The magnesium-aluminum-containing spinel-based composition may be formedinto particles of any desired shape such as pills, cake, extrudates,powders, granules, spheres, and the like using conventional methods. Thesize selected for the particles can be dependent upon the intendedenvironment in which the final discrete entities are to be used--as, forexample, whether in a fixed catalyst bed circulating catalyst bedreaction system or whether as a separate particle or as part of a massof combined particles.

Substantially non-interferring proportions of other well knownrefractory material, e.g., inorganic oxides such as silica, zirconia,thoria and the like may be included in the present discrete entities.Free magnesia and/or alumina (i.e., apart from the spinel) also may beincluded in the discrete entities, e.g., using conventional techniques.For example, the discrete entities may include about 0.1% to about 25%by weight of free magnesia (calculated as MgO). By substantially"non-interferring" is meant amounts of other material which do not havea substantial deleterious effect on the present spinel composition, thepresent catalyst system or hydrocarbon conversion process. The inclusionof materials such as silica, zirconia, thoria and the like into thepresent discrete entities may act to improve one or more of thefunctions of the discrete entities.

The added component or components may be included in the presentlyuseful discrete entities in any suitable conventional manner. Thiscomponent is preferably introduced into the discrete entities after thespinel or spinel precursor is formed. This added component isdistinguished from the alkali metal component that may be present as ininherent part of the materials used to produce the spinel or spinelprecursor during the formation of the spinel precursor. This "inherent"alkali metal component is ordinarily washed from the precursor to insureproper spinel formation and/or function. The present added component orcomponents are included in the magnesium-aluminum-containing spinelcompositions from a source or sources other than the materials used toproduce the spinel compositions. When the added component is selectedfrom alkali metal components and mixtures thereof, it is preferablypresent in an amount in the range of about 0.1% to about 15%, morepreferably about 0.25% to about 10%, by weight (calculated as elementalmetal) of the discrete entities. When the added component is selectedfrom the group consisting of calcium components, barium components,strontium components, beryllium components and mixtures thereof, it ispreferably present in an amount in the range of about 0.1% to about 25%,more preferably about 0.5% to about 20%, by weight (calculated aselemental metal) of the discrete entities.

In a preferred embodiment, the added component is associated with, e.g.,deposited on, the discrete entities after the spinel is formed. In afurther preferred embodiment, the added component is deposited on thediscrete entities using one or more impregnation techniques, e.g.,conventional techniques.

A suitable method of preparation is to impregnate a support withsolutions of compounds of the desired metals. Suitable compounds usefulfor impregnation include the acetates, acetylacetonates, oxides,carbides, carbonates, hydroxides, formates, oxalates, nitrates,phosphates, sulfates, sulfides, tartrates, fluorides, chlorides,bromides, or iodides. After impregnation the preparation is dried in anoven to remove solvent and the dried solid is prepared for use bycalcining, preferably in air at a temperature selected within the rangeof about 300° C. to 1200° C. Particular calcination temperatures willvary depending upon the particular metal compound or compounds employed.

Cerium or other suitable rare earth or rare earth mixture may beassociated with the spinel using any suitable technique or combinationof techniques; for example, impregnation, coprecipitation, ion-exchangeand the like, well known in the art, with impregnation being preferred.Impregnation may be carried out by contacting the spinel with asolution, preferably aqueous, of rare earth; for example, a solutioncontaining cerium ions (preferably Ce⁺³, Ce⁺⁴ or mixtures thereof) or amixture of rare earth cations containing a substantial amount (forexample, at least 40%) of cerium ions. Water-soluble sources of rareearth include the nitrate and chloride. Solutions having a concentrationof rare earth in the range of 3 to 30% by weight are preferred.Preferably, sufficient rare earth salt is added to incorporate about0.05 to 25% (weight), more preferably amount 2 to 15% rare earth, andstill more preferably about 3 to 12% rare earth, by weight, calculatedas elemental metal, on the particles.

It may not be necessary to wash the spinel after certain soluble rareearth salts (such as nitrate or acetate) are added. After impregnationwith rare earth salt, the spinel can be dried and calcined to decomposethe salt, forming an oxide in the case of nitrate or acetate.Alternatively, the spinel, e.g., in the form of discrete particles, canbe charged to a hydrocarbon conversion, e.g., cracking unit, with therare earth in salt form. In this case a rare earth salt with a thermallydecomposable anion can decompose to the oxide in the reactor and beavailable to associate with SOx in the regenerator.

Especially good results were achieved using spinel containing discreteentities such that the concentration of rare earth metal, e.g., cerium,calculated as the metal, is in the range of about 1% to about 25%, morepreferably about 2% to about 15%, by weight of the total discreteentities.

The present discrete entities preferably further comprise a minor amountof at least one crystalline aluminosilicate capable of promoting thedesired hydrocarbon conversion. Typical aluminosilicates have beendescribed above. Preferably, such aluminosilicates comprise about 1% toabout 30%, more preferably about 1% to about 10%, by weight of thediscrete entities. The presence of such aluminosilicate in the presentdiscrete entities acts to increase the overall catalytic activity of thesolid particles-discrete entities mixture for promoting the desiredhydrocarbon conversion.

As indicated above, in one preferred embodiment the presently usefulparticulate material, e.g., the discrete entities utilized in thepresent invention, also contain at least one additional metal, e.g.,platinum group metal, component. These additional metal components aredefined as being capable of promoting the oxidation of sulfur dioxide tosulfur trioxide at combustion conditions, e.g., the conditions presentin the catalyst regenerator. Increased carbon monoxide oxidation mayalso be obtained by including at least one of the additional metalcomponents. Such metal components may be incorporated into the presentlyuseful particulate material, e.g., the discrete entities, in anysuitable manner. Many techniques for including the additional metal inthe particulate material are conventional and well known in the art. Theadditional metal, e.g., platinum group metal, such as platinum, mayexist within the particulate material, e.g., discrete entities, at leastin part as a compound such as an oxide, sulfide, halide and the like, orin the elemental state. Generally, the amount of the platinum groupmetal component present in the final discrete entities is small comparedto the quantity of the spinel. The platinum group metal componentpreferably comprises from about 0.05 parts-per-million (ppm) to about 1%more preferably about 0.5 ppm. to about 500 ppm., by weight of thediscrete entities, calculated on elemental basis. Excellent results areobtained when the discrete entities contain about 50 ppm. to about 200ppm., and in particular about 50 ppm. to about 90 ppm., by weight of atleast one platinum group metal component. The other additional metalsmay be included in the particulate material in an amount effective topromote the oxidation of at least a portion, preferably a major portion,of the sulfur dioxide present to sulfur trioxide at the conditions ofcombustion, e.g., conditions present in the catalyst regeneration zoneof a hydrocarbon catalytic cracking unit. Preferably, the presentdiscrete entities comprise a minor amount by weight of at least oneadditional metal component (calculated as elemental metal). Of course,the amount of additional metal used will depend, for example, on thedegree of sulfur dioxide oxidation desired and the effectiveness of theadditional metal component to promote such oxidation.

Alternately to inclusion in the discrete entities, one or moreadditional metal component may be present in all or a portion of theabove-noted solid particles and/or may be included in a type of particleother than either the present solid particles or discrete entities, forexample, separate particles comprising at least one additional metalcomponent and porous inorganic oxide support, e.g., platinum on alumina,may be included along with the solid particle and discrete entities topromote sulfur dioxide oxidation.

The additional metal, e.g., platinum group metal, component may beassociated with the spinel based composition in any suitable manner,such as by the impregnation of the spinel at any stage in itspreparation and either after or before calcination of the spinel basedcomposition. As indicated previously, various procedures forincorporating the additional metal component or components into theparticulate material are conventional and well known in the art.Preferably, the additional metal component is substantially uniformlydisposed on the spinel of the present discrete entities. One preferredmethod for adding the platinum group metal to the spinel involves theutilization of a water soluble compound of the platinum group metal toimpregnate the spinel. For example, platinum may be added to the spinelby comingling the spinel with an aqueous solution of chloroplatinicacid. Other water-soluble compounds of platinum may be employed asimpregnation solutions, including, for example, ammonium chlorplatinateand platinum chloride.

Both inorganic and organic compounds of the platinum group metals areuseful for incorporating the platinum group metal component into thepresent discrete entities. Platinum group metal compounds, such aschlorplatinic acid and palladium chloride are preferred.

It may be desirable to be able to separate the discrete entities fromthe solid particles, for example, when it is desired to use the solidparticles alone for hydrocarbon conversion of where it is desired toreover the discrete entities for other uses or for example, for platinumgroup metal recovery. This can be conveniently accomplished by preparingthe second solid particles in a manner such that they have a differentsize than the first solid particles. The separation of the first andsecond solid particles can then be easily effected by screening or othermeans of size segregation.

As noted above, the presently useful solid particles and discreteentities can be employed in a mass of combined particles which functionas both the solid particles, e.g., promotes hydrocarbon conversion, andthe discrete entities. Such combined particles may be produced in anysuitable manner, certain of which methods are conventional and known inthe art.

The spinel-containing compositions of the present invention findparticular applicability in reducing sulfur oxide emissions fromcombustion zones wherein the oxygen present in the combustion zone isinsufficient to provide for complete combustion of the combustiblematerials, e.g., of the sulfur-containing carbonaceous deposit materialreferred to previously. For example, in the regeneration zone of ahydrocarbon catalytic cracking unit, oxygen is present to convertcarbonaceous material, e.g., deposited on the cracking catalyst, tocarbon dioxide, water, sulfur oxides and the like oxidized products. Incertain instances, the amount of oxygen present in such catalystregeneration zones is insufficient to completely combust thiscarbonaceous material to the fully oxidized products. In this instance,the present spinel-containing compositions provide substantial activityin reducing the sulfur content of the flue gases from the regenerationzone. In this application, it is preferred that the additional metalcomponent referred to previously not be present in association with thespinel-containing composition. Thus, these compositions, in thesubstantial absence of additional metal component, e.g., cerium, providesubstantial benefits, e.g., removal of sulfur, from combustion zones inwhich the oxygen present is insufficient to fully combust thecombustible material.

Although this invention is useful in many hydrocarbon chemicalconversions, the present catalyst, i.e., mixture comprising solidparticles and discrete entities, and process find particularapplicability in systems for the catalytic cracking of hydrocarbons andthe regeneration of catalyst so employed. Such catalytic hydrocarboncracking often involves converting, i.e., cracking, heavier or higherboiling hydrocarbons to gasoline and other lower boiling components,such as hexane, hexene, pentane, pentene, butane, butylene, propane,propylene, ethane, ethylene, methane and mixtures thereof. Often, thesubstantially, hydrocarbon feedstock comprises a gas oil fraction, e.g.,derived from petroleum, shale oil, tar sand oil, coal and the like. Suchfeedstock may comprise a mixture of straight run, e.g., virgin, gas oil.Such gas oil fractions often boil primarily in the range of about 400°F. to about 1000° F. Other substantially hydrocarbon feedstocks, e.g.,other high boiling or heavy fractions of petroleum, shale oil, tar sandoil, coal and the like may be cracked using the catalyst and method ofthe present invention. Such substantially hydrocarbon feedstock oftencontains minor amounts of contaminants, e.g., sulfur, nitrogen and thelike. In one aspect, the present invention involves converting ahydrocarbon feedstock containing sulfur and/or sulfur chemicallycombined with the molecules of hydrocarbon feedstock. The presentinvention is particularly useful when the amount of sulfur in suchhydrocarbon feedstock is in the range of about 0.01% to about 5%,preferably about 0.1% to about 3% by weight of the total feedstock.

Hydrocarbon cracking conditions are well known and often includetemperatures in the range of about 850° F. to about 1100° F., preferablyabout 900° F. to about 1050° F. Other reaction conditions usuallyinclude pressures of up to about 100 psia.; catalyst to oil ratios ofabout 1 to 2 to about 25 to 1, preferably about 3 to 1 to about 15 to 1;and weight hourly space velocities (WHSV) of from about 3 to about 60.These hydrocarbon cracking conditions may be varied depending, forexample, on the feedstock and solid particles or combined particlesbeing used and the product or products wanted.

In addition, the catalytic hydrocarbon cracking system includes aregeneration zone for restoring the catalytic activity of the solidparticles or combined particles of catalyst previously used to promotehydrocarbon cracking. Carbonaceous, in particular sulfur-containingcarbonaceous, deposit-containing catalyst particles from the reactionzone are contacted with free oxygen-containing gas in the regenerationzone at conditions to restore or maintain the activity of the catalystby removing, i.e., combusting, at least a portion of the carbonaceousmaterial from the catalyst particles. When the carbonaceous depositmaterial contains sulfur, at least one sulfur-containing combustionproduct is produced in the regeneration zone and may leave the zone withthe regenerator flue gas. The conditions at which such freeoxygen-containing gas contacting takes place may vary, for example, overconventional ranges. The temperature in the catalyst regeneration zoneof a hydrocarbon cracking system is often in the range of about 900° F.to about 1500° F., preferably about 1100° F. to about 1350° F. and morepreferably about 1100° F.to about 1300° F. Other conditions within suchregeneration zone may include, for example, pressures up to about 100psia., average catalyst contact times within the range of about 3minutes to about 120 minutes, preferably from about 3 minutes to about75 minutes. Sufficient oxygen is preferably present in the regenerationzone to completely combust the carbon and hydrogen of the carbonaceousdeposit material, for example, to carbon dioxide and water. The amountof carbonaceous material deposited on the catalyst in the reaction zoneis preferably in the range of about 0.005% to about 15%, more preferablyabout 0.1% to about 5% by weight of the catalyst. The amount ofcarbonaceous material deposited on the catalyst in the reaction zone ispreferably in the range of about 0.005% to about 15%, more preferablyabout 0.1% to about 10%, by weight of the catalyst. The amount ofsulfur, if any, contained in the carbonaceous deposit material depends,for example, on the amount of sulfur in the hydrocarbon feedstock. Thisdeposit material may contain about 0.01% to about 10% or more by weightof sulfur. At least a portion of the regenerated catalyst is oftenreturned to the hydrocarbon cracking reaction zone.

The solid particles useful in the catalytic hydrocarbon crackingembodiment of the present invention may be any conventional catalystcapable of promoting hydrocarbon cracking at the conditions present inthe reaction zone, i.e., hydrocarbon cracking conditions. Similarly, thecatalytic activity of such solid particles is restored at the conditionspresent in the regeneration zone. Typical among these conventionalcatalysts are those which comprise amorphous silica-alumina and at leastone crystalline aluminosilicate having pore diameters of about 9A toabout 15A and mixtures thereof. When the solid particles and/or discreteentities to be used in the hydrocarbon cracking embodiment of thepresent invention contain crystalline aluminosilicate, the crystallinealuminosilicate may include minor amounts of conventional metalpromoters such as the rare earth metals, in particular, cerium.

As indicate previously, one embodiment of the present invention involvescontacting solid, sulfur-containing meterial in a combustion zone atcombustion conditions to produce combustion products including at leastone sulfur oxide at least a portion of which is sulfur trioxide. Reducedemissions of sulfur oxide from the combustion zone are achieved bycarrying out this contacting in the presence of discrete entities asdefined herein.

Typical solid material combustion zones include, for example, fluid bedcoal burning steam boilers and fluid sand bed waste combustors. Thepresent discrete entities have sufficient strength to withstand theconditions in such combustion zones. In the coal fired boilerapplication, the discrete entities are added, either separately or withthe sulfur-containing coal, to the combustion zone, e.g., boiler, wherecombustion takes place and at least some sulfur trioxide is formed. Thediscrete entities leave the combustion zone with the coal ash and can beseparated from the ash, e.g., by screening, density separation, or otherwell known solids separation techniques. The flue gases leaving thecombustion zone have reduced amounts of sulfur oxide, e.g., relative tocombustion in the absence of the discrete entities. The discreteentities from the combustion zone can then be subjected to a reducingenvironment, e.g., contacted with H₂, at conditions such that at least aportion of the sulfur associated with the discrete entitiesdisassociates with the discrete entities, e.g., in the form of H₂ S, andis removed for further processing, e.g., sulfur recovery. The discreteentities, after sulfur removal may be recycled to the combustion zone,e.g., boiler.

Conditions within the boiler may be those typically used in fluid-bedcoal burning boilers. The amount of discrete entities used is sufficientto reduce sulfur oxide emissions in the boiler flue gas, preferably, byat least about 50% and more preferably by at least about 90%. Conditionswithin the reducing zone are such that at least a portion, preferably atleast about 50% and more preferably at least about 80% of the sulfurassociated with the discrete entities is removed. For example, reducingconditions may include temperatures in the range of about 900° F. toabout 1800° F.; pressures in the range of about 14 to about 100 psia;and H₂ to associates sulfur mole ratio in the range of about 1 to about10.

In the fluid sand bed waste combustion application, the fluid sand,e.g., which acts as a heat sink, may be combined with the discreteentities and circulated from the combustion zone to the reduction zone.Reduced emissions of sulfur oxide from the combustion zone are thusachieved.

Conditions in the combustion zone may be as typically employed in fluidsand bed waste combustors. The amount of discrete entities employed issufficient to reduce sulfur oxide emissions to the combustor flue gases,preferably by at least about 50% and more preferably by at least about80%. Conditions within the reducing zone are similar to those set forthabove for the coal fired boiler application.

The following examples are provided to better illustrate the invention,without limitation, by presenting several specific embodiments of theprocess of the invention.

EXAMPLE I

The base spinel precursor was prepared using the following procedure.

Magnesium nitrate hexahydrate (166.7 g., 0.65 mole) was dissolved in 325ml. water. The acidity was adjusted by slowly adding 26 ml. (0.41 mole)of concentrated nitric acid.

Sodium aluminate (Nalco) (142.8 g., 0.65 mole Al₂ O₃ and 0.71 mole Na₂O) was separately dissolved in 425 ml. water.

The sodium aluminate solution was added, with stirring, to the magnesiumnitrate solution over a period of 1 hour. The resulting aqueous slurrypH was monitored and was brought to a pH of 9.5 by dropwise addition of20% NaOH solution. After stirring for an additional hour, the slurry waspermitted to age quiescently for 16 hours at ambient temperature.

The slurry was filtered, washed with water to remove sodium ion, and thewashed filter cake dried at 260° F. for 16 hours in a forced air forcedair oven. The dried product was ground to pass through 60-mesh screen.

EXAMPLE II

A portion of the dried product produced in accordance with Example I wascalcined by heating gradually to 1350° F. over 4 hours and being held atthat temperature in a flowing air stream for an additional 3 hours. Thiscalcined spinel base was impregnated with aqueous cerium nitrate using aconventional incipient wetness technique. The impregnated material wascalcined at 1350° F. for 3 hours in a flowing air stream, following agradual heat-up to that temperature. The sodium content of this calcinedproduct was about 0.09% by weight. The calcined product also contained10% by weight of cerium, calculated as elemental cerium.

EXAMPLE III

Another portion of the dried product produced in accordance with ExampleI was impregnated with an aqueous solution of sodium nitrate using aconventional incipient wetness technique. This impregnated material wasdried for 16 hours at 260° F., then calcined at 1350° F. for 3 hours ina flowing air stream, following a gradual heat up to that temperature.This calcined material contained 0.91% by weight of sodium.

EXAMPLE IV

Another portion of the dried product produced in accordance with ExampleI was impregnated with an aqueous solution of calcium nitrate hydrateusing a conventional incipient wetness technique. This impregnatedmaterial was dried for 16 hours at 260° F., then calcined at 1350° F.for 3 hours in a flowing air stream, following a gradual heat up to thattemperature. This calcined material contained 5.84% by weight ofcalcium.

EXAMPLE V

Another portion of the dried product produced in accordance with ExampleI was impregnated with an aqueous solution of barium nitrate using aconventional incipient wetness technique. This impregnated material wasdried for 16 hours at 260° F., then calcined at 1350° F. for 3 hours ina flowing air stream, following a gradual heat up to that temperature.This calcined material contained 1.87% by weight of barium.

EXAMPLE VI to VIII

Each of the calcined products from Examples III, IV and V wasimpregnated with an aqueous solution of cerium nitrate using aconventional incipient wetness technique. The impregnated materials werethen calcined at 1350° F. for 3 hours in a flowing air stream, followinga gradual heat-up to that temperature. Each of the resulting materialscontained 10 wt. % cerium, calculated as elemental cerium.

EXAMPLE IX

Spinel-containing compositions of the preceding Examples II, VI, VII andVIII, after dilution to 1.0-1.75 wt. % with equilibrium, commerciallyavailable fluid catalytic cracking catalyst (FCC catalyst), were testedfor sulfur pick-up capabilities as follows. Each of these materials wasfluidized in a gas stream, comprising (by volume) 5.9% O₂, 1.5% SO₂ and92.6% N₂, after heating at 1350° F. in a stream of nitrogen gas. After a15-minute treatment with the SO₂ -containing gas, remaining SO₂ wasflushed out with nitrogen. After cooling, analyses for sulfur wereconducted on the solids and on the gas stream to determine theefficiency of SOx pickup by formation of metal sulfates. These materialswere found to have a substantial capability to pick-up sulfur as shownin Table I.

EXAMPLE X

The sulfur-containing, spinel-containing compositions from Example IXwere heated to 1350° F. in flowing nitrogen gas and then for 5 minutesin a stream of hydrogen. Each spinel composition was flushed withnitrogen, and, after cooling, as analyzed for sulfur content, todetermine the efficiency of sulfur removal by reduction of metalsulfates. Each of these materials was found to have a substantialcapability to release sulfur under the conditions of the above-notedtreatment.

EXAMPLE XI

Portions of the mixtures of FCC catalyst and spinel compositionsprepared in Example IX were steamed (prior to being tested in accordancewith the procedures of Examples IX and X) as follows: The mixture wascharged into a quartz reactor, where it was heated under nitrogenpressure to 1400° F. at which time 100% steam was introduced. After 6hours, the steam was stopped and nitrogen introduced. The mixture waskept at temperature for 15-20 minutes, then allowed to cool. The mixturewas then tested for sulfur pick-up in accordance with Example IX(results shown in Table I) and for sulfur release in accordance withExample X. Each of these steamed materials was found to have asubstantial capability to pickup and release sulfur under the conditionsof the above-noted treatments.

                  TABLE I.sup.1                                                   ______________________________________                                                         SOx                                                          Composition.sup.2                                                                              Pickup, % Activity.sup.3                                     ______________________________________                                        From Example II  76        35                                                 Steamed          22         9                                                 From Example VI  69        55                                                 Steamed          26        11                                                 From Example VII .sup. --.sup.4                                                                          .sup. --.sup.4                                     Steamed          59        31                                                 From Example VIII                                                                              66        52                                                 Steamed          39        20                                                 ______________________________________                                         .sup.1 The FCC catalyst employed had a minor SOx pickup activity which wa     taken into account in the SOx pickup data shown below. Thus, these data       reflect the actual SOx pickup of the mixture of FCC catalyst plus             composition of Example.                                                       .sup.2 As blend of 1.25 wt. % of the composition prepared in the Example      in FCC catalyst (except for Example I).                                       ##STR1##                                                                      .sup.4 Data not available.                                               

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims:

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a process forcombusting solid, sulfur-containing material by contacting said materialwith oxygen in a combustion zone at combustion conditions to producecombustion products including at least one sulfur oxide, the improvementcomprising carrying out said contacting in the presence of discreteentities containing at least one magnesium-aluminum-containing spinel,and a minor amount of at least one added component selected from thegroup consisting of alkali metal components, calcium components, bariumcomponents, strontium components, beryllium components and mixturesthereof, said discrete entities being present in an amount sufficient toreduce the amount of sulfur oxide leaving said combustion zone, and saidadded component is introduced into said discrete entities after saidspinel or the precursor to said spinel is formed.
 2. The process ofclaim 1 wherein said discrete entities further comprise at least onerare earth metal component.
 3. The process of claim 1 wherein saiddiscrete entities contains a major amount by weight of said spinel andsaid spinel has a surface area of about 25 m.² /gm. to about 600 m.²/gm.
 4. The process of claim 1 wherein said discrete entities furthercomprise a minor, catalytically effective amount of at least oneadditional metal component capable of promoting the conversion of sulfurdioxide to sulfur trioxide at said combustion conditions.
 5. The processof claim 4 wherein said additional metal component is at least oneplatinum group metal component.
 6. The process of claim 2 wherein saiddiscrete entities further comprise a minor, catalytically effectiveamount of at least one additional metal component capable of promotingthe conversion of sulfur dioxide to sulfur trioxide at said combustion.7. The process of claim 6 wherein said additional metal component is atleast one platinum group metal component.
 8. The process of claim 1wherein said added component is selected from the group consisting ofalkali metal components and mixtures thereof and is present in an amountin the range of about 0.25 to about 10% by weight of the discreteentities.
 9. The process of claim 1 wherein said added component isselected from the group consisting of calcium components, bariumcomponents, strontium components, beryllium components and mixturesthereof and is present in an amount in the range of about 0.1% to about25% by weight of the discrete entities.
 10. The process of claim 1wherein said discrete entities contain at least about 70% by weight ofsaid spinel.
 11. The process of claim 1 wherein said discrete entitiescontain at least about 90% by weight of said spinel.
 12. The process ofclaim 2 wherein said rare earth metal component comprises cerium. 13.The process of claim 2 wherein said rare earth metal component is ceriumcomponent and is present in an amount of about 1% to about 25% by weightof said discrete entities.
 14. The process of claim 1 wherein the amountof oxygen provided to said combustion zone is insufficient to fullycombust said solid, sulfur-containing material.
 15. In a hydrocarbonconversion process for converting a sulfur-containing hydrocarbonfeedstock which comprises: (1) contacting said feedstock with solidparticles capable of promoting the conversion of said feedstock athydrocarbon conversion conditions in at least one reaction zone toproduce at least one product and to cause deactivating sulfur-containingcarbonaceous material to be formed on said solid particles therebyforming deposit-containing particles; (2) contacting saiddeposit-containing particles with oxygen at conditions to combust atleast a portion of said carbonaceous material in at least oneregeneration zone to thereby regenerate at least a portion of thehydrocarbon conversion catalytic activity of said solid particles and toform a regeneration zone flue gas; and (3) repeating step (1) and (2)periodically, the improvement which comprises: using, in intimateadmixture with said solid particles, a minor amount of discrete entitieshaving a composition different from said solid particles and comprisingat least one magnesium-aluminum-containing spinel, and a minor amount ofat least one added component selected from the group consisting ofalkali metal components, calcium components, barium components,strontium components, beryllium components and mixtures thereof, saiddiscrete entities being present in an amount sufficient to reduce theamount of sulfur oxides in said flue gas, and said added component isintroduced into said discrete entities after said spinel or theprecursor to said spinel is formed.
 16. The process of claim 15 whereinsaid conversion comprises hydrocarbon cracking in the substantialabsence of added molecular hydrogen, said solid particles and discreteentities being fluidizable and circulating between said reaction zoneand said regeneration zone.
 17. The process of claim 16 wherein theamount of oxygen provided to said regeneration zone is insufficient tofully combust said sulfur-containing carbonaceous material.